1. Field of the Invention
The present invention relates to a thermal transfer recording apparatus in which an image is recorded on a recording medium by heating a transfer medium having an ink and transferring the ink to the recording medium.
Some examples of thermal transfer recording apparatus of the type mentioned above are an electronic typewriter, a facsimile apparatus, a copying machine, and a printer. Examples of images which may be recorded by the apparatus include numeric characters, characters, and graphics. Further, recording media which may be used in the apparatus include, in addition to ordinary paper and converted paper, plastic sheets for use in OHPs.
2. Related Background Art
While information-related industries have rapidly developed in the recent years, various types of information processing systems have been developed, and various recording methods suited for these various types of systems have also been developed.
One of these recording methods is a thermal transfer recording method in which a recording head generates heat in accordance with an image signal to record the image. More specifically, such a thermal transfer recording method comprises causing a recording head having resistors which generate heat when supplied with electricity to generate heat in accordance with an image signal, heating an inked sheet coated with a heat-transferable ink by the recording head in a pattern corresponding to the image, and transferring the ink to a recording paper.
Since the principle of thermal transfer recording is simple, an apparatus for recording an image based on this principle is advantageous in various aspects. For instance, a thermal transfer recording apparatus can be compact and be manufactured with low cost, while it can operate with very low noise being generated.
A known thermal transfer recording apparatus, however, has a drawback in terms of durability of the recording head. For instance, if such an apparatus is used for a long period, electrodes of the recording head may be destroyed, thus making it impossible to supply electricity to the heat generating resistors.
The present inventor has conducted various studies on this problem and has found that the cause of the destruction of the electrodes of the recording head is electrochemical reactions in the electrodes of the recording head which are caused by electric current flowing through the inked sheet and the recording head when they are brought into contact with each other. More specifically, the electrodes of the recording head are corroded by the electrochemical reactions and are thereby disconnected, and this makes any supply of electricity to the heat generating resistor impossible. As a result, the recording head will have a very short life. Although a recording head of a thermal transfer recording apparatus is usually covered with a protective film made of, for instance, SiO.sub.2 or Ta.sub.2 O.sub.5, such a protective film sometimes fails to prevent the electrochemical reactions from affecting the surface of the electrodes of the recording head.